This invention relates to a blade-type tensioner having a blade shoe with a chain sliding face and a blade spring for application of spring force onto the blade shoe.
FIG. 6 shows one example of a conventional blade tensioner, used for tensioning an associated chain. As shown in the figure, conventional blade tensioner 100 includes a blade shoe 101 of resin that extends in a curved line form, multiple blade springs 102 that extend along blade shoe 101 and are attached onto the blade shoe, and a metal bracket 120 as the bracket member that supports blade shoe 101.
Projection 110, having curved face 110a, is formed at the tip of blade shoe 101 and the projection 110 has concavity 111 that stores one end of blade spring 102. A nearly triangular projection 112 is formed at the fixed end end of blade shoe 101 and a concavity 113, that stores the other end of blade spring 102, is formed in the projection 112.
Holes for attaching, 121, 122, are formed in bracket 120. Sliding face 125, on which projection 110 at blade shoe tip 101 can contact and slide, is formed at the tip of bracket 120. One end of pin 130 is fixed at the center of bracket 120. Projection 112, as the fixed end side of blade shoe 101, is inserted rotatably onto pin 130.
During. operation of the chain, the chain runs on sliding face 101a of blade shoe 101 and the press-down load, due to blade shoe 101 and deformation of blade spring 102, acts on the chain at such time. The conventional blade tensioner is used where the center-to-center distance of the chain is relatively short, such as a chain to drive the oil pump of an engine. On the other hand, because of the demand to lower the cost of the engine, it is desired to use a blade tensioner of relatively low manufacturing cost, for a cam chain that drives between the crankshaft and the camshaft.
In the case of a cam chain, the center distance is long, generally, so that the length of the blade tensioner needs to be long to match the center distance. However, when the total length of the blade tensioner is long, the resonant frequency becomes low due to its lower natural frequency and, as a result, the blade tensioner resonates within the rpm range of the engine and fatigue damage can occur.
This invention addresses such a conventional problem. The objective is to offer a blade tensioner that can prevent resonance in the rpm range and fatigue damage.
It is a first aspect of the invention to provide a blade tensioner which applies tension to a chain. The tensioner includes a blade shoe with a chain sliding face, a blade spring that applies the spring force to the blade shoe and a bracket upon which to attach the blade shoe. A fixed end, portion, or proximal end of the blade shoe is rotatably attached to the bracket. The blade spring contacts the tip or distal end of the bracket at a contact point located between the free end and the fixed end of the blade shoe.
In this invention, the chain runs on the chain sliding face of the blade shoe. Proper tension is applied to the chain by the action of the blade shoe activated by the force of the deformed blade spring. The natural frequency of the blade tensioner is determined by the location where the tip of the bracket and the blade spring come into contact. As the contact point between the spring and the bracket moves toward the tip of the blade shoe, the natural frequency of the shoe becomes lower. On the other hand, as the contact point moves toward the fixed end of the blade shoe, the natural frequency of the shoe and tensioner becomes higher. The objective is to raise the natural frequency of the blade tensioner higher than the frequency of vibrations generated by the engine.
In the present invention, the location of the contact point between the tip portion of the bracket and blade spring or blade shoe is located between the blade shoe tip or free end and its fixed end, so that the natural frequency of the blade tensioner is made relatively high. Thereby, the resonant frequency of the blade tensioner can be set relatively high compared to those frequencies generated by the engine and, as a result, the resonance of the blade tensioner within the rpm range of the engine can be prevented and fatigue damage due to resonance can be prevented.
It is a second aspect of the invention to provide a blade tensioner that applies tension force to the chain and includes a blade shoe with a chain sliding face, a blade spring that applies a spring force to the blade shoe, and a bracket to which the blade shoe is attached. The fixed end of the blade shoe is rotatably attached to the bracket. The length of the blade spring is shorter than the length of the sliding face of the blade shoe. A first end of the blade spring is attached to the fixed end of the blade shoe and the second end is located apart from the blade shoe and, at the same time, the second end slidably contacts the tip of the bracket. The overall length of the blade spring is shorter than the length of the sliding face of the blade shoe and the second end of the blade spring (i.e. the tip), located apart from the blade shoe, slides on the tip of the bracket. The tip of the bracket is in contact with the second end of the blade spring and the position of this contact point is located between the free and the fixed ends of the blade shoe and, in one example, it is offset from a mid position between the ends of the blade shoe and located nearer to the blade shoe tip.
In this manner, the resonance frequency of the blade tensioner can be set high and, as above, the resonance in the engine rpm range and fatigue damage due to resonance can be prevented.
It is a third aspect of the invention to provide a blade tensioner with a further or second blade spring that runs along the face opposite the chain sliding face of the blade shoe. Thus, the deformation per unit load is small. That is, a blade tensioner with a high spring constant is offered.
It is a fourth aspect of the invention to provide a blade tensioner with a free end or second end of the blade spring curved with the curved face slidably contacting the tip of the bracket. Thus, there is no interference with the bracket tip and deformation of the blade spring is smooth.
It is a fifth aspect of the invention to provide a blade tensioner to apply tension to the chain including a blade shoe with a chain sliding face and a blade spring that is provided on the side opposite the chain sliding face of the blade shoe. The blade spring applies the spring force onto the blade shoe. A bracket is provided on which to attach the blade shoe. The fixed end of the blade shoe is rotatably attached to the bracket. An outward projection is formed at the tip of the bracket or on the blade shoe, at a location approximately midway between the free end of the blade shoe and its fixed end. The projection is adapted to slide on the blade spring or the tip of the bracket depending on whether it is formed on the bracket or the blade shoe.
An outward projection is formed between the tip and fixed end of the blade shoe and the projection slidably contacts the blade spring or bracket tip. The projection at the bracket tip contacts the blade spring or the projection on the blade shoe side contacts the bracket tip and this contact point is located approximately midway between the blade shoe free end and its fixed end. Thereby, the resonance frequency of the blade tensioner can be set high and, as above, the resonance in the engine rpm range and fatigue damage due to the resonance can be prevented.
It is a sixth aspect of the invention to provide a blade tensioner with a projection. The projection has a curved face and the curved face slidably contacts the tip of the bracket or the blade spring. The projection formed on the blade shoe can have a curved face and this curved face slidably contacts the blade spring or bracket tip, thereby deformation of the blade spring can be smooth.
It is a seventh aspect of the invention to provide a blade tensioner which applies a force to the chain and includes a blade shoe with a chain sliding face, a blade spring to apply the spring force onto the blade shoe, and a bracket on which the blade shoe is rotatably attached. The blade spring includes a first blade spring that is provided on the side opposite to the chain sliding face of the blade shoe and a second blade spring which is shorter than the chain sliding face, a first end of which is attached to the fixed end of the blade shoe and the second end is positioned away from the blade shoe. At the same time, the other end of the second blade spring is attached to the projection that is provided to the bracket.
The projection of the bracket contacts the second or free end of the second blade spring and this point of contact is located between the blade shoe free end and its fixed end. Thereby, the resonance frequency of the blade tensioner can be set high and the resonance in the engine rpm range and resulting fatigue damage are prevented.
It is an eighth aspect of the invention to provide a blade tensioner which has a projection on the bracket with a curved portion. The curved portion or face slidably contacts the first blade spring and the projection has an attachment portion or part to which the other end of the second blade spring can be slidably attached.
It should be understood that some embodiments of the present invention contemplate use of a protrusion formed on either the shoe or the bracket portion of the tensioner adapted to bear upon the other element. The protrusion can be located between the ends of the element (the shoe or bracket) upon which it is formed. The location of the protrusion defines the location of the point of contact between the shoe and the bracket. It can be seen that as the point of contact between the shoe and bracket is moved from a location near the middle of the shoe to the end of the shoe the free span of tensioner shoe thus created is lengthened and thus, the natural resonant frequency of the shoe becomes lower. It is therefore an object of the invention to locate the point of contact between the shoe and the bracket via the protrusion operating therebetween at a middle location between the ends of the shoe. Thus, the natural frequency of the shoe is maintained at a higher frequency relative to lower engine vibrations and reduces the susceptibility of the tensioner to damage from resonant vibrations originating from the engine and associated mechanisms.
For a more complete understanding of the invention, one should refer to the embodiments illustrated in greater detail in the drawings and described below by way of examples of the invention.